Generac Generator Sizing Guide - ask-the-electrician.com

G en e rator Sizi ng guide

IMPORTANT NOTICE:

This booklet is designed to familiarize estimators and installers with proper sizing guidelines for residential and commercial generators. The information is not comprehensive, nor does it replace or supercede any material contained in any of the written documents shipped with the equipment. This booklet should only be used in conjunction with the Owner's Manual, Installation Manual and other technical documents shipped with each product. Always read all accompanying documentation carefully before attempting to install any generator, transfer switch or related equipment.

HOW TO USE THIS BOOKLET:

Within this booklet, you will find electrical load information, plus an outline of generator surge capability, fuel pipe sizing, liquid propane tank sizing, and UPS / generator compatibility. The final pages are perforated for easy removal and can be photocopied to create additional Onsite Estimating Sheets for use with individual jobs.

SAFETY INFORMATION:

Proper sizing of the generator is crucial to the success of any installation and requires a good working knowledge of electricity and its characteristics, as well as the varying requirements of the electrical equipment comprising the load. When analyzing the electrical load, consult the manufacturer's nameplate on each major appliance or piece of equipment to determine its starting and running requirements in terms of watts, amps and voltage. When choosing the generator output for commercial or industrial applications, select a rating that is approximately 25% higher than the peak load (for example, if the load is about 40 kilowatts, select a 50 kW genset). A higher rated generator will operate comfortably at approximately 80% of its full capacity and will provide a margin of flexibility if the load increases in the future.

For safety reasons, Generac recommends that the backup power system be installed, serviced and repaired by a Generac Authorized Service Dealer or a competent, qualified electrician or installation technician who is familiar with applicable codes, standards and regulations.

It is essential to comply with all regulations established by the Occupational Safety & Health Administration (OSHA) and strict adherence to all local, state and national codes is mandatory. Before selecting a generator, check for municipal ordinances that may dictate requirements regarding placement of the unit (setback from building and/or lot line), electrical wiring, gas piping, fuel storage (for liquid propane or diesel tanks), sound and exhaust emissions.

If you have a technical question regarding sizing or installation, contact Generac's Technical Service Center toll free at 888-GENERAC during normal business hours (8 a.m. to 5 p.m. CST).

G en e rator Sizi ng guide

Table 1 motor load reference

AC & Heat Pumps

Running Load

RunningAmps atAmps atAmps atStarting

Description

Hp

kW

240V 1? 208V 3? 480V 3?

kW

Starting Load

LR Amps LR Amps LR Amps at 240V 1? at 208V 3? at 480V 3?

1 Ton (12,000 BTU)11

5313

2517

7

2 Ton (24,000 BTU)

2

210

73

6

503314

3 Ton (36,000 BTU)331510

4

9

75

50

22

4 Ton (48,000 BTU)

4

4

2013

612100

67

29

5 Ton (60,000 BTU)

5

5

2516

715125

8336

7.5 Ton (85,000 BTU)

7.5

7.537

241117188125

54

10 Ton (120,000 BTU)

5 Hp (x2)10

49331415125

8336

10 Ton (120,000 BTU)10 Hp10

493314

20

250167

72

15 Ton (180,000 BTU)

7.5 Hp (x2)15

74

49

2117188125

54

15 Ton (180,000 BTU)15 Hp15

74

49

2130375

250108

20 Ton (240,000 BTU)10 Hp (x2)

20

98

65

28

20

250167

72

20 Ton (240,000 BTU)

20 Hp

20

n/a

65

28

40

500333144

25 Ton (300,000 BTU)

25

25

n/a

8235

50

625

416180

30 Ton (360,000 BTU)15 Hp (x2)30

n/a

98

4230375

250108

30 Ton (360,000 BTU)30 Hp30

n/a

98

42

60

750

500

217

40 Ton (480,000 BTU)

20 Hp (x2)

40

n/a131

57

40

500333144

40 Ton (480,000 BTU)

40 Hp

40

n/a131

57

801000

666

289

50 Ton (480,000 BTU)

25 Hp (x2)

50

n/a163

71

50

625

416180

50 Ton (480,000 BTU)

50 Hp

50

n/a163

711001250

833361

General Residential

Running LoadStarting Load

Description

Hp

RunningAmps atAmps atStarting

kW

120V 1? 240V 1?

kW

LR Amps LR Amps 120V 1? 240V 1?

Refrigerator, Sump Pump, Furnace, Garage Opener

0.5

0.5

4.9

2.51.5

2513

Freezer, Washer, Septic Grinder

0.75

0.75

7.43.7

2.33819

General 1 Hp11

9.8

4.93

50

25

Well & Septic Lift Pump

2

219.6

9.8

6100

50

G en e r ato r Si z ing g u i d e

Table 2 NON-MOTOR LOAD REFERENCE

General Residential

Running Load

Amps at Amps at

Description

kW

120V 1?

240V 1?

Electric heat per 1000 ft.212

n/a

50

Heat pump elements per 1000 ft.2

7

n/a

29

Dryer

5.5

n/a

23

Hot tub

5

n/a

21

Range oven

5

n/a

21

Hot water

4.5

n/a19

Stove top per burner1.5

n/a

6

General receptacles per 1000 ft.21

8.3

n/a

Lighting per 1000 ft.2

0.75

6.3

n/a

Blow dryer1.2510.4

n/a

Dishwasher1.512.5

n/a

Microwave1

8.3

n/a

Toasters1

8.3

n/a

G en e rator Sizi ng guide

Table 3 surge capability

Generac QT Series Generators Operating at < 3600 RPM

Rated OutputSurge CapabilitySurge Capability

(Running Amps) LR Amps at 15% Voltage Dip LR Amps at 30% Voltage Dip

Size (kW)

240V 1?

208V 3?

480V 3?

240V 1?

208V 3?

480V 3?

240V 1?

208V 3?

480V 3?

25104

8738

71

47

26133

89

52

30125104

45113

75

43

225150

87

40167139

60129

86

49

254169

97

55

229191

83196130

76392

261150

70

292

243105

275183106

550366

212

80333

278120

275183106

550366

212

100

417347150371

247142

738

491

284

130

542

451195

546364

2091088

724

419

Generac QT Series Generators Operating at 3600 RPM

Rated OutputSurge CapabilitySurge Capability

(Running Amps) LR Amps at 15% Voltage Dip LR Amps at 30% Voltage Dip

Size (kW)

240V 1?

208V 3?

480V 3?

240V 1?

208V 3?

480V 3?

240V 1?

208V 3?

480V 3?

7

29

2411

23

n/a

n/a

46

n/a

n/a

10

42351531

n/a

n/a

63

n/a

n/a

13

54

45

2038

n/a

n/a

75

n/a

n/a

16

67

56

24

46

n/a

n/a

92

n/a

n/a

20

83

6930

63

42

24121

80

47

25104

8738

71

47

26138

92

53

35146121

53104

69

40

204136

78

45188156

68146

97

57

292194112

50

208173

75146

97

57

292194112

60

250

208

90179119

69354

236136

70

292

243105

246164

95

496330190

100

417347150333

222128

663

441

255

150

625

520

226

558372

2151121

747

431

Note: All kW models listed above are based on nominal LP rating.

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